1. Field of the Invention
The present invention relates to disposing liquid crystal within a liquid crystal display panel.
2. Description of the Related Art
Portable electronic devices such as mobile phones, personal digital assistants (PDA), and notebook computers often require thin, lightweight, and efficient flat panel displays. There are various types of flat panel displays, including liquid crystal displays (LCD), plasma display panels (PDP), field emission displays (FED), and vacuum fluorescent displays (VFD). Of these, LCDs have the advantages of being widely available, easy to use, and possessing superior image quality.
With characteristic advantages of excellent image quality, lightness, slim size, and low power consumption, LCD, one of the panel devices, has been widely used so as to replace CRT (cathode ray tube) as a mobile image display. Besides the mobile usage for a monitor of a notebook computer, LCD is also developed as a monitor for computer, television, or the like so as to receive and display broadcasting signals.
In spite of various technical developments to perform a role as an image display in various fields, an effort to improve image quality of LCD inevitably becomes contrary to the above characteristics and advantages in some aspects. In order to use LCD for various fields as a general image display, the development of LCD depends on the facts that the characteristics of lightness, slim size, and low power consumption are maintained and that image of high quality including definition, brightness, large-scaled area, and the like is realized properly.
Such an LCD is mainly divided into a liquid crystal display panel displaying an image thereon and a driving unit applying a drive signal to the liquid crystal display panel, in which the liquid crystal display panel includes first and second glass substrates bonded to each other so as to have a predetermined space therebetween and a liquid crystal layer injected between the first and second glass substrates.
The LCD device displays information based on the refractive anisotropy of liquid crystal. As shown in FIG. 1, an LCD 10000 includes a lower substrate 10005, an upper substrate 10003, and a liquid crystal layer 10007 that is disposed between the lower substrate 10005 and the upper substrate 10003. The lower substrate 10005 includes an array of driving devices and a plurality of pixels (not shown). The individual driving devices are usually thin film transistors (TFT) located at each pixel. The upper substrate 10003 includes color filters for producing color. Furthermore, a pixel electrode and a common electrode are respectively formed on the lower substrate 10005 and on the upper substrate 10003. Alignment layers are formed on the lower substrate 10005 and on the upper substrate 10003. The alignment layers are used to uniformly align the liquid crystal layer 10007.
The lower substrate 10005 and the upper substrate 10003 are attached using a sealing material 10009. In operation, the liquid crystal molecules are initially oriented by the alignment layers, and then reoriented by the driving device according to video information so as to control the light transmitted through the liquid crystal layer to produce an image.
The fabrication of an LCD device requires the forming of driving devices on the lower substrate 10005, the forming of color filters on the upper substrate 10003, and disposing liquid crystal in a cell process (described subsequently) between the lower substrate 10005 and the upper substrate 10003. Those processes as typically performed in the prior art will be described with reference to FIG. 2.
Initially, in step S11101, a plurality of perpendicularly crossing gate lines and data lines are formed on the lower substrate 10005, thereby defining pixel areas between the gate and data lines. A thin film transistor that is connected to a gate line and to a data line is formed in each pixel area. Also, a pixel electrode that is connected to the thin film transistor is formed in each pixel area. This enables driving of the liquid crystal layer according to signals applied through the thin film transistor.
In step S11104, R (Red), G (Green), and B (Blue) color filter layers (for reproducing color) and a common electrode are formed on the upper substrate 10003. Then, in steps S11102 and S11105, alignment layers are formed on the lower substrate 10005 and on the upper substrate 10003. The alignment layers are rubbed to induce surface anchoring (thereby establishing a pretilt angle and an alignment direction) for the liquid crystal molecules. Thereafter, in step S11103, spacers for maintaining a constant, uniform cell gap is dispersed onto the lower substrate 10005.
Then, in steps S11106 and S11107, a sealing material is applied to outer portions such that the resulting seal has a liquid crystal injection opening. The opening is used to inject liquid crystal. The upper substrate 10003 and the lower substrate 10005 are then attached together by compressing the sealing material.
While the foregoing has described forming a single panel area, in practice it is economically beneficial to form a plurality of unit panel areas. To this end, the lower substrate 10005 and the upper substrate 10003 are large glass substrates that contain a plurality of unit panel areas, each having a driving device array or a color filter array that is surrounded by sealant having a liquid crystal injection opening. To isolate the individual unit panels, in step S11108 the assembled glass substrates are cut into individual unit panels. Thereafter, in step S11109 liquid crystal is injected into the individual unit panels by way of the liquid crystal injection openings, which are then sealed. Finally, in step S11110 the individual unit panels are tested.
As described above, in the prior art liquid crystal is injected through a liquid crystal injection opening. Injection of the liquid crystal was usually pressure induced. FIG. 3 shows a prior art device for injecting liquid crystal. As shown, a container 10012 that contains liquid crystal, and a plurality of individual unit panels 10001 are placed in a vacuum chamber 10010 such that the individual unit panels 10001 are located above the container 10012. The vacuum chamber 10010 is connected to a vacuum pump that generates a predetermined vacuum. A liquid crystal display panel moving device (not shown) moves the individual unit panels 10001 into contact with the liquid crystal 10014 such that each injection opening 10016 is in the liquid crystal 10014.
When the pressure within the chamber 10010 is increased by inflowing nitrogen gas (N2), the liquid crystal 10014 is injected into the individual unit panels 10001 through the liquid crystal injection openings 10016. After the liquid crystal 10014 entirely fills the individual unit panels 10001, the liquid crystal injection opening 10016 of each individual unit panel 10001 is then sealed by a sealing material.
While the prior art technique described above is generally successful, there are problems with pressure injecting liquid crystal 10014. First, the time required for the liquid crystal 10014 to inject into the individual unit panels 10001 is rather long. Generally, the gap between the driving device array substrate and the color filter substrate is very narrow, on the order of micrometers. Thus, only a very small amount of liquid crystal 10014 is injected per unit time. For example, it takes about 8 hours to inject liquid crystal 10014 into an individual 15-inch unit panel 10001. Increasing the size of the individual unit panel 10001, say to a 24-inch unit panel, dramatically increases the already excessive time (to more than twenty hours) that is required to inject the liquid crystal.
Second, the prior art technique requires an excessive amount of liquid crystal 10014. For example, consider that only a small amount of liquid crystal 10014 in the container 10012 is actually injected into the individual unit panels 10001. However, since liquid crystal 10014 exposed to air or to certain other gases can be contaminated by chemical reaction, the remaining liquid crystal 10014 in the container 10012 should be discarded. This increases liquid crystal fabrication costs.
Therefore, an improved method and apparatus for applying a liquid crystal between substrates would be beneficial.